Inhibition of corrosion by hydrotreater effluent

ABSTRACT

Corrosion of metals by aqueous hydrochloric acid condensates in petroleum processing equipment is markedly inhibited by the addition of a lower aliphatic amine to the system. The operative amines are primary aliphatic amines having four to 10 carbon atoms. Octylamine is a preferred inhibitor.

Unite States aiei Forouhs [451 July 1 1, 1972 [54] INHIBITION OFCORROSION BY References Cited HYDROTREATER EFFLUENT UNITED STATESPATENTS [72] Inventor: Zisis Andrew Foroulis, East Orange, NJ. 2,938,8515/1960 Stedman et a], ..208/47 2,920,030 1/ 1960 Thompson 73 l iResearch and Engmeer'ng cmpany 3,447,891 6/1969 Crawford ..21/2.5 [22]Filed: Feb. 19, 1970 Primary Examiner-Delbert E Gantz [21] Appl 12340Assistant Examiner-G. E. Schmitkons AttorneyPearlman and Stahl and LouisF. Kreek, Jr. [52] US. Cl ..208/47, 21/2.7, 21/58,

106/14, 203/7, 208/209, 208/262, 252/148, ABSTRACT 252/390 1 2;}Elsi-fear -;,,g ;g gg;v;g;;g 532;:rgzsilxzeiozzsigsgi:iiizirizzrkssiiizziifa; 5 2 2 by the addition of a lower aliphaticamine to the system. The

operative amines are primary aliphatic amines having four to 10 carbonatoms. Octylamine is a preferred inhibitor.

6Claims,NoDrawings INHIBITION OF CORROSION BY HYDROTREATER EFFLUENTBACKGROUND OF THE INVENTION This invention relates to the inhibition ofcorrosion of metal vessels used in petroleum processing operations byaqueous acidic constituents of the petroleum process stream. Moreespecially, this invention relates to the inhibition of corrosion in theeffluent from a hydrotreating unit caused by condensation of corrosiveaqueous acidic constituents in said effluent.

Hydrotreating is an operation which is used widely in the petroleumprocess industry for reducing the sulfur content of a feedstock and forimproving various properties of the feedstock such as color, odor, andstability. Basically, hydrotreating comprises treating ahydrocarbonaceous feedstock with hydrogen in the presence of a catalystunder comparatively mild conditions which will not cause significantrupture of carbon to carbon linkages as is characteristic ofhydrocracking and reforming. Typical reactions taking place include theconversion of mercaptans and disulfides to hydrogen sulfide andhydrogenation of olefins to paraffins. Solvent hydrocarbons are amongthe feedstocks which can be treated in this manner. Hydrotreated solventstocks must generally meet severe standards of color, odor, andcorrosiveness. Such solvents may be used for various purposes, includinguse as an extractant in food processing. Use in food processing requiresthat the solvent be nontoxic, in addition to the aforementionedproperties.

A great problem in hydrotreating is the condensation of aqueoushydrochloric acid in the effluent from the hydrotreater. Petroleumproducing operations frequently utilize organic chlorinated compounds ascarbon tetrachloride and trichloroethylene. These compounds distilloverhead into the naphtha stream in petroleum processing operationswhich precede or hydrotreating unit and thus are contained in thehydrotreater feedstock. It is common practice to cool the hydrotreatereffluent, which results in the condensation of water on metal surfacesof heat exchangers, condensers, and the like. Sufficient hydrolysis ofthe chlorinated carbon compounds occurs to form hydrogen chloride, whichdissolves in the water condensate to form highly acidic and highlycorrosive aqueous hydrochloric acid condensate. These condensatesusually have a pH of less than about 4, and frequently may have a pH ASlow as 1 OR even less. Since the corrosion rate of metals, andparticularly ferrous metals, by acids rises rapidly as the pH isdecreased below 4, it will be appreciated that a very severe corrosionproblem exists in the effluent circuit of a hydrotreater.

Acidic substances such as aqueous hydrochloric acid condensates willcause severe corrosion of metals from which conventional petroleumrefining equipment is constructed. Carbon steels, such as 1020 carbonsteel containing 0.2 percent carbon, are used predominantly as materialsof construction. While it would be possible to fabricate refineryequipment from steels which are less prone to corrosive attack, such asstainless steels and special alloy steels, the cost of such equipmentwould be inordinately high and would make any process being conductedwith such equipment uneconomical.

It is therefore essential to provide a corrosion inhibitor which willcontrol corrosion and make possible the use of carbon steel asconstruction material for equipment such as piping, heat exchangers, andthe like.

The choice of a corrosion inhibitor for the effluent circuit of asolvent hydrotreater is restricted by the fact that the hydrotreatedsolvent must be nontoxic, colorless and odorlesss for many industrialapplications of said solvents. This rules out a number of inhibitorswhich give effective corrosion inhibition. It is therefore essential toprovide a corrosion inhibitor which not only gives effective corrosioninhibition, but

which is also either nontoxic, colorless and odorless, or is removablefrom the hydrotreated effluent by simple procedures such as washing,which will yield an acceptable quality of hydrotreated solvent.

SUMMARY OF THE INVENTION It has been found that corrosion of metalvessels containing a petroleum process stream by aqueous acidiccondensates in said stream can be inhibited by adding to the processstream a corrosion inhibiting amount of a primary aliphatic aminecontaining from 4 to 10 carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION The corrosion inhibitors of thepresent invention, as above indicated, are the primary aliphatic amineshaving from 4 to 10 carbon atoms. The alkyl amines are preferred. Theeffective inhibitors of this invention have boiling points of at least50 C. (144 F.) to about 300 C. (572 F.). The inhibitors of the presentinvention may be represented by the structural formula RNH Where R is analkyl radical containing from four to 10 carbon atoms.

The aliphatic amines containing four to 10 carbon atoms are unexpectedlybetter corrosion inhibitors than higher molecular weight primary amines,such as dodecyl amine. Furthermore, the aliphatic amines containing fourto 10 carbon atoms do not impart any odor or color to the hydrocarbonproduct when used in a hydrocarbon processing system. Furthermore, theseamines are nontoxic and are easily removable from the hydrocarbonproduct by acid washing, which permits them to be used as corrosioninhibitors even when the product hydrocarbon is to be used as anextracting agent or solvent in many industrial applications where theseproperties are desirable.

The preferred corrosion inhibitor of this invention is n-octylamine. Itsboiling point is above that of water, so that it condenses beforecorrosive condensates form and thereby protects metal surfaces fromcorrosion. Other primary aliphatic amines having from four to 10 carbonatoms can also be used advantageously as corrosion inhibitors.Butylamine, for example, gives outstanding corrosion protection; it isless preferred than octylamine because its boiling point is below thatof water, and therefore it does not condense with corrosive condensatesas effectively as do the higher molecular weight amines.

Primary amines having more than 10 carbon atoms are avoided, becausethey are less effective as corrosion inhibitors than the primary amineshaving four to 10 carbon atoms, and because they impart an undesirableodor, and in the case of the higher molecular weight amines (e.g.,octadecylamine), impart an undesirable color also to hydrocarbonproducts.

Any metals which are subject to acid attack can be protected with theinhibitors of this invention. This inhibitors are particularly usefulfor protection of ferrous metals, and especially low carbon steel, suchas 1020 carbon steel (containing 0.2 percent carbon). Low carbon steelsare ideal for construction of petroleum processing equipment from thestandpoint of cost and other significant qualities such as strength andtheir ability to withstand the process stream temperatures. Theprincipal drawback to low carbon steel is its susceptibility to acidcorrosion, and problems arising from this are substantially obviated bythe use of the inhibitors of this invention.

Nonoxidative corrosion by acids is ordinarily a problem where the pH ofthe acidic solution is about 4 or lower. The amine inhibitors of thisinvention offer excellent protection even in solutions which aredecidedly on the acid side, e.g., those having a pH of 1 or lower.

The inhibitors of the present invention are particularly useful ininhibiting corrosion in hydrotreating operations. The inhibitor isintroduced into the hydrotreater effluent prior to cooling thereof. Whenthe effluent is cooled and condensation takes place, the corrosioninhibitor protects the equipment against corrosion caused by suchcondensates.

While ferrous metals have been cited as an illustrative example ofmetals which can be protected according to this invention, it should beunderstood that other metals and alloys, such as nickel and stainlesssteels, may also be protected.

The problem of corrosion attack is most severe in those vessels, such ascondensers, heat exchangers, and transfer lines, where water condenses.The acid gases present in the process stream are dissolved in thecondensate, and attack the metal process equipment. It has been foundthat the corrosion inhibitors herein are effective under the entiretemperature range in which water is present in the liquid phase. Sincesome processes are run at high pressure, the actual temperature may beconsiderably above the atmospheric boiling point of water; neverthelessthe inhibitors do not lose their effectiveness at such temperatures.Likewise, they remain effective at low temperatures down to 32 F.

The present invention will be more fully described with reference to thefollowing specific example. It is understood than this example is anillustration of a specific embodiment of this invention and is not to betaken as limiting.

EXAMPLE This example will illustrate the effectiveness of aliphaticamines as inhibitors of acid induced corrosion of 1020 carbon steelexposed to 0.1 N hydrochloric acid, having a pH of 1.1. Corrosion testsin this example were conducted at 200 F. Corrosion rates were measuredby weight losses, carbon steel specimens having a size of approximately1 inch X 4 inches X Va inch, and a surface area of approximately 58square centimeters. The specimens were abraded through 4-0 emery paper,degreased in benzene, and washed in distilled water. Immediately afterdrying, the specimens were weighed and placed in a corrosion cell andimmersed in the corrosive solution. Each of the corrosive solutions,except those used for control purposes, contained a predeterminedconcentration of an aliphatic amine. The amount of corroded metal wasdetermined by weight loss. The corrosion cell was basically a 2000 M/LErlenmeyer flask with a special top to permit entrance and exit ofnitrogen for deaeration and to provident air contamination. The cell hada removable chimney with Pyrex hooks from which the metal specimens weresuspended. The corrosive solution was deaerated with nitrogen beforeeach run. Nitrogen also was bubbled through the solution continuouslyduring a run to prevent contamination with air. A con stant temperaturewas achieved by the use of a constant temperature oil bath. All runswere carried out for 2 days at a constant temperature of 200 F.

The results of representative experiments utilizing the above procedureare summarized below in Table I. In this table, corrosion rate inmilligrams per square decimeter per day (mg./dm. /day or mdd.) andpercentage inhibitor efficiency which equals (l,,-I,)/(L,) X 100, wherei is the corrosion rate without inhibitor and l, is the corrosion ratewith inhibitor) are given for various concentrations of inhibitor.Concentration in Table I below is given as the weight percentage of theinhibitor in the corrosive test solution. All corrosion rates are theaverage of two runs.

TABLE I Concen- Corrosion 7: ln- Adverse tration Rate hibitor Efiect oninhibitor Wt. mg./dm."'/ effic- Odor Color day iency Blank 2160Butylamine 1.5 5.0 99.8 No No Octylamine 1.5 32.5 98.7 No No Octylamine3.0 14.2 99.3 No No *Dodecylamine 1.5 463 78.5 Yes No *Dodecylamine 3.033.3 98.1 Yes No *Octadecylamine 3.0 274 87.: Yes Yes *Given forcomparison purposes.

What is claimed is: 1. A process for inhibiting corrosion of metalvessels by aqueous acidic condensates having a pH not greater than about4 m a hydrotreater effluent stream, which comprises adding to saidstream a corrosion inhibiting amount of a saturated primary aliphaticamine containing from 4 to 10 carbon atoms.

2. A process according to claim 1 in which said aqueous acidiccondensate is aqueous hydrochloric acid.

3. A process according to claim 1 in which said amine is octylamine.

4. A process according to claim 1 in which the concentration of saidamine is at least about l.5 percent by weight of the acidic condensate.

5. A process according to claim 1 in which the metal is a ferrous metal.

6. A process according to claim 5 in which said ferrous metal is carbonsteel.

2. A process according to claim 1 in which said aqueous acidiccondensate is aqueous hydrochloric acid.
 3. A process according to claim1 in which said amine is octylamine.
 4. A process according to claim 1in which the concentration of said amine is at least about 1.5 percentby weight of the acidic condensate.
 5. A process according to claim 1 inwhich the metal is a ferrous metal.
 6. A process according to claim 5 inwhich said ferrous metal is carbon steel.